LM3209-G3_15 Datasheet, PDF (16/22 Pages) Texas Instruments – LM3209-G3 Seamless-Transition Buck-Boost Converter for Battery-Powered 3G/4G RF Power Amplifiers

LM3209-G3
SNVS626B – NOVEMBER 2009 – REVISED MARCH 2013
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OUTPUT CAPACITOR SELECTION
Use a 4.7 µF, 6.3V, X7R, X5R, or B types; do not use Y5V or F. DC bias characteristics of ceramic capacitors
must be considered. DC bias characteristics vary from manufacturer to manufacturer, and DC bias curves should
be requested from them as part of the capacitor selection process.
The output filter capacitor smooths out current flow from the inductor to the load, helps maintain a steady output
voltage during transient load changes and reduces output voltage ripple. These capacitors must be selected with
sufficiency capacitance and low ESR to perform these functions. Note that the output voltage ripple is dependent
on the inductor current ripple and the Equivalent Series Resistance of the output capacitor (ESR). The ESR is
frequency dependent (as well as temperature dependent); make sure the value used for calculations is at the
switching frequency of the part.
10 µF for C_IN
4.7 µF for C_OUT
Table 3. SUGGESTED CAPACITORS
Model
C1608X5R0J106K
ECJ1VB0J475K
GRM188R60J475ME84D
GRM219R61A475KE19
Vendor
TDK
Panasonic
Murata
Murata
RECOMMENDED EXTERNAL COMPONENT COMBINATIONS FOR VCON TRANSIENT
Achieving optimum Output Voltage (VCON) Transient is expected to require both an inductor with smaller
inductance degradation and an output capacitor with modest capacitance. FDK MIPSZ2520D2R2 and Panasonic
ECJ1VB0J475K are one sample of the external component combination.
An inductor with a large inductance drop at high DC bias causes slower charging current to the output capacitor.
An output capacitor with less capacitance drop at high voltage will cause a big overshoot. However, an output
capacitor with a large capacitance drop generates bigger output voltage ripple.
DSBGA PACKAGE ASSEMBLY AND USE
Use of the DSBGA package requires specialized board layout, precision mounting and careful re-flow
techniques, as detailed in Texas Instruments Application Note 1112. Refer to the section Surface Mount
Technology (SMD) Assembly Considerations. For best results in assembly, alignment ordinals on the PC board
should be used to facilitate placement of the device. The pad style used with DSBGA package must be the
NSMD (non-solder mask defined) type. This means that the solder-mask opening is larger than the pad size.
This prevents a lip that otherwise forms if the solder-mask and pad overlap, from holding the device off the
surface of the board and interfering with mounting. See Application Note 1112 for specific instructions how to do
this.
The 12-bump package used for LM3209-G3 has 300 micron solder balls and requires 10.82 mil pads for
mounting on the circuit board. The trace to each pad should enter the pad with a 90° entry angle to prevent
debris from being caught in deep corners. Initially, the trace to each pad should be 7 mil wide, for a section
approximately 7 mil long, as a thermal relief. Then each trance should neck up or down to its optimal width. The
important criterion is symmetry. This ensures the solder bumps on the LM3209-G3 re-flow evenly and that the
device solders level to the board. In particular, special attention must be paid to the pads for bumps A3, B3, and
D3. Because PVIN and PGND are typically connected to large copper planes, inadequate thermal relief can
result in late or inadequate re-flow of these bumps.
The DSBGA package is optimized for the smallest possible size in applications with red or infrared opaque
cases. Because the DSBGA package lacks the plastic encapsulation characteristic of larger devices, it is
vulnerable to light. Backside metallization and/or epoxy coating, along with front-side shading by the printed
circuit board, reduce this sensitivity. However, the package has exposed die edges. In particular, DSBGA
devices are sensitive to light (in the red and infrared range) shining on the package's exposed die edges.
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